Field of the Invention
The present disclosure relates to a method and an apparatus for an interference alignment and a multi-antenna signal processing in a multi-cell random access wireless network environment such as a wireless LAN, and more particularly, to a method and an apparatus for an interference alignment and a multi-antenna signal processing in a wireless communication system on a multi-cell random access wireless network configured of access points having a plurality of antennas and user terminals having different numbers of antennas.
Description of the Related Art
As shown in FIG. 1, in a wireless communication system configured of K transmitters (Tx) and K receivers (Tx) in a multi-cell wireless network environment, an interference between channels occurs when each cell of each transmitter (Tx) transmits a message. A research for improving the degree of freedom, and the transmission rate for a multi-cell wireless network by analyzing a model for the interference channel has been progressed.
The degree of freedom of a corresponding K-user interference channel in the K transmitters (Tx) and K receivers (Tx) environment of FIG. 1 may be represented by Equation 1. Here, the SNR is a signal-to-noise ratio, and the Csum (SNR) is a sum of a transmission capacity of total interference channel.
                                          SNR            →            ∞                    lim                ⁢                                            C              sum                        ⁡                          (              SNR              )                                            log            ⁢                                                  ⁢            SNR                                              [                  Equation          ⁢                                          ⁢          1                ]            
That is, the degree of freedom of interference channel is a key measure to determine the magnitude of a transmission gain in comparison with a single user in a large SNR area.
As shown in FIG. 1, since the wireless channel has a characteristic of receiving a signal of the transmitter (Tx) by all receivers, with respect to the case of transmitting a message to a specific separated receiver (Rx) by the transmitter (Tx), many experts predicted that the degree of freedom (DoF) of K-user interference channel is 1.
However, beyond the predictions of many experts, the Syed Jafar research group of University of California, Irvine derived a new interference control paradigm called an interference alignment in 2008, and it turned out that the degree of freedom in the K-user interference channel like FIG. 1 is K/2. For example, in a wireless communication system as shown in FIG. 1, four separated data stream may be transmitted by using the interference alignment in the 3-user interference channel (k=3), that is, the degree of freedom 4/3 may be achieved.
Interference alignment that began as a signal space interference alignment based on a beam forming is developed to a technique such as a real interference alignment, an ergodic interference alignment, and the like by many research groups. Further, an improved method for improving the degree of freedom as users are increased is required in consideration of uplink or downlink in a multi-cell or a single-cell wireless network environment. In addition, in a carrier sense multiple access (CSMA) random access environment, or an orthogonal frequency division multiplexing (OFDM) environment, although a research on opportunistic random access technique which induces a user having a large channel gain to access first an access point stochastically by controlling a backoff time of a user terminal is progressed, an improved method for improving the degree of freedom as users are increased is required.